ROME -- Tiscali SpA agreed to buy British Internet-service provider LineOne for 100 million euros ($89.5 million), marking its second cross-border acquisition this week and leading it to claim status as Europe's biggest Internet communications firm.

Tiscali, founded on the island of Sardinia in 1997, is paying 80 million euros in stock and 20 million euros in cash for LineOne, an ISP and portal company owned by British...